When 'Status' field picklist value changes from Open to Closed, I would like to calculate days on 'Duration' field and update 'WO Date' fields at a time using either workflow or process builder in Salesforce. Any solutions??
Workflow and Process Builder can both cause multiple actions to be triggered on a single set of criteria, see images for this. Workflow rules configuring actions and considerations. Process Builder documentation.
These actions can include field updates, creating a task sending email alerts and outbound messages.
If there is a dependency on one action for the other action to execute then it may be necessary to add an additional step in Process Builder or a separate Workflow rule.